I will update this guide, i maybe think taht magic resist is better than flat AP

Upvoted a nice guide really epic to read xD.

I have few things to comment why starting with Amplifying Tome and Flap AP seals? I know you are not addressing this guide to high elo ranked games, but even a guy with 300 wins knows morde sucks early. you are an easy kill if you get caught by jungler. In addiciton Morde's shield early sucks it's great for end game when you are tough enough to absorb more than one enemies's skill, but an AA on lv 1 will crush your shield. Lich Bane is great for late game and Zephyr is a good idea. Remove Warmog's Armor please it makes me cry.

Good job +1.

A possible substitute for lichbane could be iceborn gauntlets because your gunblade gives you more ad for it's passive, it slows in an area of affect (Only really good if you didnt pick of ryleias) and it provides good armor seeing morde is an off tank, or could be your teams only tank. And it takes care of that pesky useless mana. Just a tip :).

Most people would say your carry build is bad, and i agree with them somehow (because u are squishy), but i must tell u i use same build as u do :D
Except i would take Nashor's Tooth instead of Zhonya's Hourglass.

Here's why:
If u take Zhonya's Hourglass u will get even more AP and some durability, but in fact its better for morde if u take some cooldown reduction item, like Nashor's Tooth. More spell u can deal in less time, more passive shield will u get.
That means: more spells=more damage=more shield=more durable in teamfights
But u must be careful, because this build cant take heavy bursts of damage or too much crowd control.

Try this out sometime and good luck! ;)

Cant be total tank, he need a little bit AP so Rylai is good choice.

You're right in that Morde can't support, but he can't be a full tank either